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Air Inlet
Max. Length
Model
No.
Certified
Venting
Material
Vent Size
Maximum
Equivalent
Vent Length*
Combustion
Air
Intake Pipe
Material
6” 8”
302B 5”
402B
100’ N/A
502B
6”
75’
652B
752B
40’
100’
902B
Category III
8”
70’
Room Air
40’
Ducted
Combustion
Air
Galvanized
Steel,
PVC,
ABS,
CPVC
30’ 80’
Table M: Category III Horizontal and Direct Venting
Use only the special gas vent pipes listed for use with
Category III gas burning heaters, such as the AL29-4C
stainless steel vents offered by Heat Fab Inc. (800-
772-0739), Protech System, Inc. (800-766-3473),
Z-Flex (800-654-5600) or American Metal Products
(800-423-4270). Pipe joints must be positively sealed.
Follow the vent manufacturer’s installation instructions
carefully.
Direct Vent - Horizontal Through-
the-Wall
Installation
These installations utilize the heater-mounted blower
to draw combustion air from outdoors and vent com-
bustion products to the outdoors.
Note: When vertical height exceeds 25 ft,
consult factory prior to installation.
Fig. 26: Direct Vent - Horizontal Through-the-Wall
The total length of the through-the-wall flue cannot
exceed 40 equivalent ft in length for the flue outlet.
Each elbow used is equal to 10 ft of straight pipe. This
will allow installation in one of the three following
arrangements:
• 40’ of straight flue pipe
• 30’ of straight flue pipe and one elbow
• 20’ of straight flue pipe and two elbows.
The total length of air supply pipe cannot exceed the
distances listed in Table M. Each elbow used is equal
to 10 ft of straight pipe. This will allow installation in
any arrangement that does not exceed the lengths
shown in Table M.
The flue direct vent cap is not considered in the over-
all length of the venting system.
Care must be taken during assembly that all joints are
sealed properly and are airtight.
The vent must be installed to prevent the potential ac-
cumulation of condensate in the vent pipes. It is
required that:
1. The vent must be installed with a slight downward
slope of not more than 1/4 inch per foot of hori-
zontal run to the vent terminal.
2. The vent must be insulated through the length of
the horizontal run.
* Subtract 10 ft per elbow. Max. 3 elbows.
Maximum combustion air duct length terminated at 100 equivalent ft.